An apparatus for the treatment of filtration sludges in which kieselgur or diatomaceous earth constitutes the major solid component as a result of the use of the diatomite in the filtration process as a filtration aid, generally comprises a feed device for finely distributing the filtration sludge into a flow-drying unit for the drying and dispersing thereof into a flow of gas. The resulting granular product is separated from the drying flow in a cyclone and filter unit and is subjected to treatment in a high-temperature treatment chamber with a treatment gas stream, the treatment gas stream being separated from the treated product which can then be cooled.
The term "treatment" is used herein to refer to a treatment of the diatomite which will allow a problem-free disposal of the solid residues in a landfill, i.e. landfill disposal without subsequent environmental problems. It also refers to a regeneration which allows the treated product to be used as a filter aid.
Kieselgur or diatomite is a mineral product (see Rompps Chemie-Lexikon, 1973, 1770) which is used as a filter aid in various industries. For example, it may be used in the sugar industry, in the brewery field and in the chemical and pharmaceutical industries to provide a filter mass and to serve as an adsorbent for various organic contaminants.
Apart from the various kieselgurs or diatomites which are employed for this purpose, the filter aid can include other filtration auxiliaries in the inert dry mass. These can include expanded or blown perlite or expanded or blown vermiculite.
The filtration sludge can contain, apart from these filtration aids, various substances deposited on the solid particles. These substances are predominantly of an organic nature and make the treatment necessary.
The quantities of perlite and vermiculite generally are present in only several percent by weight. They serve to provide greater stability of the fine particulate mass against mechanical stresses.
The filtration sludge can also include silica gel which is frequently used in contact processes together with kieselgur.
Of course, the precise compositions of filter sludges will depend on how they were produced.
When reference is made herein to dispersing of the filtration sludge, I mean to describe a breakup of the dispersion solution to primary particles or granules. When filtration sludges which derive from brewery processes are employed, the process should be able to produce a treated product which can be reused as a brewery filter aid. In that sense the invention should be considered to be capable of providing a closed circulation for the kieselgur and diatomite.
In the processes which have been used heretofore, the treatments did not always give rise to satisfactory reusable products or products which could be subjected to safe prolonged landfill disposal. In earlier system a transformation of noncrystalline silicic acid contained in the kieselgur to crystalline silicic acid has been observed. This has been found to be detrimental to the reuse of the treated product as a filtration aid.
Furthermore, the conventional apparatus as described has been found to require improvement since problems have been observed therein as a result of agglomeration and detrimental deposit formation, especially in the filter unit through which the drying gas must pass. These problems are of greater significance when filter sludges of different origins are treated. Furthermore, the conventional apparatus has been found to have an inordinately high energy demand, to require extensive gas cleaning, and to create problems with respect to release of the gas into the environment.